The invention relates to a method for transmitting traffic information relating to a road traffic network from a traffic information control center to at least one terminal, and to apparatuses for carrying out the method.
Traffic information is.usually transmitted from a traffic information control center to a terminal wirelessly (by radio). The relatively low and expensive radio transmission capacities mean that compressed coding is necessary.
The person skilled in the art is familiar with the practice of using RDS transmission methods (RDS-TMC) for traffic information. RDS (radio data system) relates to the transmission of digital alphanumeric information via a radio channel, similar to the transmission of Teletext information via television channels. When traffic information is transmitted using RDS-TMC, tables associating defined segments of all the relevant roads with particular codes for transmission are usually used in the traffic control center and in the terminal. This has the advantage of a very short transmission sequence for a road section, but has the drawbacks of relatively expensive terminals which are reliant on the implementation of the above tables, and of transmissions tied to the table codes of the segments.
By contrast, DE 197 50 786 A1 discloses the practice of using geographical location coordinate data given in a form compressed on a prescribed basis, and using additional location data representing roads, for example by means of text statements (xe2x80x9cA8xe2x80x9d), to transmit traffic information with the geographical location coordinates of segments indicated in traffic information which is to be transmitted. This transmission method has the advantage that it can be used even on very inexpensive traffic information terminals. With suitably coded transmission, it is also conceivable for transmission to be in the form of a short message to normal mobile radio terminals for display there in a text field of sufficient size. A drawback in this case is the relatively large quantity of data which needs to be transmitted (on account of the additional location data transmitted) as compared with the referencing of road sections on the basis of the above RDS-TMC method.
The document EP 0 725 505 A1 describes a radio receiver for receiving and for managing and reproducing digitally coded traffic reports containing location details and event details. The digitally coded traffic reports received are supplied to a device for decoding, with location-related data necessary for decoding the traffic reports being stored on an interchangeable data medium. Reproduction data can be derived from the decoded traffic reports, with further location-related data required for deriving the reproduction data being stored on the interchangeable data medium. The reproduction data can be supplied to a reproduction device.
It is an object of the present invention to provide a transmission method for traffic information which permits both compressed transmission (with a small quantity of information to be transmitted, as in the above RDS-TMC method) and transmission of traffic information in a form which can be decoded by simple terminals.
The inventive embodiment of the transmission method and of the terminals and traffic information control centers using the transmission channel for this purpose permits selective transmission of traffic information either using location coordinate data which are produced using a location coordinate table and directly represent the location coordinates of traffic segments which are to be transmitted (and possibly additional information, like the name of traffic segments or traffic segment sections, such as xe2x80x9cA8xe2x80x9d or xe2x80x9cA8, Munich/Pasing exit), or using segment identities coded with a segment table which is available in a control center without direct (direct=can be determined without table of location and identities) statement of the geographical location of said segments. The terminal is able to determine the type of coding for the received, transmitted traffic information (that is to say whether it is segment identity data using location coordinate data or using the identity of segments for the purpose of representation) on the basis of the selection information transmitted in the traffic information. The selection information is expediently indicated in the form of a flag in the transmitted traffic information.
The transmitting step may include transmitting in two transmission cycles which are shifted in time with respect to each other. Transmission within each transmission cycle is effected using only one coding including either location coordinate data or segment identity data such that a first cycle uses one of the location coordinate data or segment data and a second coding uses the other of the location coordinate data or segment data.
Further features and advantages of the invention can be found in the subclaims and in the description below of an exemplary embodiment with reference to the drawing.